class StringUtil{
  static underlineToCamel (underline) {
    let [first, ...res] = underline.split('_')

    return first + res.map(str => str[0].toUpperCase() + str.slice(1)).join('')
  }
}


console.log(StringUtil.underlineToCamel('hello_world_my_friend'))
console.log(StringUtil.underlineToCamel('good'))